How to cut sphere with sphere? Topology problem
It's possible to avoid much work here with simple inset. It won't provide great topology straight away, it will add loopcut all over the corners where sharpening is needed in order to add Subsurf.



When you have a letter just after the Boolean chances are it looks something like tris, lack of continous loops etc. Select the part with indentations (the one you'd like to sharpen out):



Invert the selection (most likely face selection will be the most comfortable). It's also possible to use Outset option by pressing O while Inset is active; then insetting will happen outwards and this step should be skipped:



Then inset with I. There will be some areas where inset will create self-intersecting geometry, some cleaning work will be needed. However it might not be necessary to do it for all the letter (although it all depends on the final result as always):